Counter flow genka head

ABSTRACT

This extruder for extruding plastic coverings over cores, or for extruding a mass of plastic having an annular cross-section and hollow interior, has passages to the extruder die correlated so that the plastic material around the entire circumference of the core travels for substantially the same length of flow path in reaching the outlet of the die. This avoids difference in pressure at different locations around the core and produces a uniform thickness of the extruded covering. The uniform length of flow passage leading to all parts of the core circumference is obtained by a combination of branch and different direction flow passages between the delivery from the extruder screw and the annular outlet of the die.

[451 June 5, 1973 [54] COUNTER FLOW GENKA HEAD David Arnold Kaye,lO932-104th Avenue N., Largo, Fla. 33540 [22] Filed: Nov. 12, 1970 [21]Appl. No.: 88,632

[76] Inventor:

[56] References Cited UNITED STATES PATENTS 7/1971 Henrikson et al...425/113 9/1954 Huckfeldt..... 9/1962 Stenger 12/ l 970 Moss ..425/114X Primary ExaminerJ. Spencer Overholser Assistant Examiner-Ben D. ToborAttorney-Sandoe, Hopgood & Calimafde [57] ABSTRACT This extruder forextruding plastic coverings over cores, or for extruding a mass ofplastic having an annular cross-section and hollow interior, haspassages to the extruder die correlated so that the plastic materialaround the entire circumference of the core travels for substantiallythe same length of flow path in reaching the outlet of the die. Thisavoids difference in pressure at different locations around the core andproduces a uniform thickness of the extruded covering. The uniformlength of flow passage leading to all parts of the core circumference isobtained by a combination of branch and different direction flowpassages between the delivery from the extruder screw and the annularoutlet of the die.

10 Claims, 7 Drawing Figures COUNTER FLOW GENKA HEAD In conventionalextruders, the plastic material is forced into the extruder cross-headunder high pressure and travels through a passage to an annular outletof the extruder die. If the plastic material is fed into the extrudercross-head from the top, then the lower part of the die outlet isfurther from the supply inlet than is the top part of the die outlet;and there is more pressure drop in the flow of the plastic material tothe lower part of the die outlet. This results in greater pressureextruding the plastic material over the upper part of the core than overthe lower part, the pressure becoming progressively lower around thesides of the core from top to bottom. More plastic is extruded where thepressure is higher and this makes covering eccentric and of nonuniformthickness.

It has been the practice of the prior art to give the die an eccentricrelation to the core with the die opening narrower where the flow pathfor the plastic material is shorter and the die opening wider wherethere is more pressure drop in the material supplied to the die opening.The eccentricity of the die can be adjusted to compensate fordifferences in the flow path, but the problem has been that thecompensation does not remain constant. For example, adjustments thatwill initially compensate for eccentricity of the extruded covering failto do so as production progresses, predominantly because of varyingcompound temperatures and viscosity.

In practice, temperatures and viscosity cannot be kept constant and theeccentricity of coverings vary so much that it is not uncommon for thecovering to fail to comply with production standards. This results insubstantial scrap losses. A more serious problem is that it is oftenimpossible to detect the extent of the eccentricity until it is too lateto make compensatory die adjustments.

The object of this invention is to provide improved flow paths for thecompound within the cross-head, thereby insuring that the velocity andpressure of the compound upon arriving at the opening in the extrudeddie is uniform about the circumference of the die opening. This producescoverings of uniform wall thickness about the core regardless ofvariations in temperature and viscosity of the extruded material.

Other objects, features and advantages of the invention will appear orbe pointed out as the description proceeds.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, forming a part hereof,in which like reference characters indicate corresponding parts in allthe views;

FIG. 1 is a sectional view through a conventional extruder of the priorart illustrating the problem to which the present invention is directed;

FIG. 2 is a sectional view taken on the line 22 of FIG. 1;

FIG. 3 is a sectional view corresponding to FIG. 1 but showing theimproved construction of this invention;

FIG. 4 is a sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is a sectional view taken on the line 5-5 of FIG. 3; and

FIGS. 6 and 7 are sectional views taken on the lines 66 and 77,respectively, of FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 shows an extruder 10 having abarrel 12 containing a conventional extruder delivery screw 14 whichadvances the plastic compound 16 through a strainer plate 18 at thedelivery end of the barrel 12. Beyond the strainer plate 18, thematerial 16 passes through a passage 20 ofa cross-head 22 which containsa helicoid 24 that surrounds a core guide 26. The helicoid 24 is held inthe cross-head 22 by a retaining nut 28 threaded into the cross-head 22;and the core guide 26 is held in the helicoid by a retaining nut 30threaded into the retaining nut 28.

There is a shoulder 32 on the helicoid 24; and to the right of thisshoulder, in FIG. 1, the diameter of the helicoid is less than thediameter of the opening through the cross-head in which the helicoid ispositioned. This leaves an annular passage 34, best shown in FIG. 2,around which the plastic material 16 flows on its way to a die 36. Thedie 36 has a frustoconical end face 38 that confronts a frusto-conicalend face 40 of the core guide 26. The angle of these faces is differentso that the passage formed by the clearance between the faces 38 and 40tapers to a narrow annular die outlet 42 where the core 44 comes throughthe end of the core guide 26. The diameter of the die is larger thanthat of the core 44 which it surrounds, the clearance being equal to thedesired wall thickness of the cover 46 which is extruded over the core44.

The construction thus far described is conventional and it will beapparent from aninspection of FIG. 1 that the flowpath for the material16 which eventually reaches the lower part of the core 44 is much longerthan the flowpath of the material which is extruded over the upper partof the core 44. This difference in flowpath results in a difference inpressure drop of the plastic material 16 being supplied to differentregions of the extruder die outlet 42 and the difference in deliveredpressure of the plastic from the die 42 results in a difference invelocity of discharge of the material 16 with a larger amount ofmaterial deposited on the upper part of the core 44 and progressivelyless material deposited on the core around the sides and toward thebottom of the core.

FIG. 3 shows a cross-head assembly made in accordance with thisinvention. It is supplied with plastic material under high pressure froman extruder barrel 12' containing an extruder delivery screw 14' thatdelivers plastic under high pressure through a strainer plate 18', theseparts of the extruder being the same as in FIG. 1 and indicated by thesame reference characters with a prime appended.

The material discharged through the strainer plate l8'enters a passage50 in a fitting 52 which is threaded into a cross-head assembly 54. Thecross-head assembly 54 includes a cross-head 56 and a helicoid 58 whichfits into the cross-head 56 and against a shoulder 60. The helicoid 58is held in place by a retaining nut 62 threaded into one end of thecross-head. A core guide 64 is inserted into the cross-head 56 from theother end and this core guide extends into the helicoid 58 with anannular clearance between a tapered face of the core guide 64 and aconfronting tapered face 66 of the helicoid 58.

The core guide has a shoulder 68 which contacts with a complementaryshoulder in the cross-head 56. The,

core guide is held against this shoulder 68 by a core guide retainingnut 70. The counterbore 72,in which the end of the core guide 64 isheld, is of larger diameter thanthe corresponding part of the coreguide-and the concentricity of the core guide 64 in the counterbore 72is adjusted by adjusting means 74 located at angularly spaced regionsaround the circumference of the cross-head 56.

The core guide 64 has a converging end portion 78 with a tapered outsideface that confronts a corresponding frusto-conical face 80 of anextrusion die 82.

The taper of the face 80 is different from the taper of the outside faceof the end portion 78 of the core guide so as to form a constrictingpassage terminating in a die outlet 84 from which the material 16' isextruded as a cover 86 over the core 88.

The die 82 is held in place by a die retaining nut 90 which screws intothe helicoid retaining nut 62. The retaining nut 90 has an annularextension 92 surrounding the circumference of the die 82 and thisannular extension 92 retains a tapered filler element 94 in the helicoid58. The filler 94 provides an extension of the inner face 66 of thehelicoid 58.

The helicoid 58 has two branch passages 96 which are formed by groovesin the outside surface of the helicoid. These grooves 96 meet at theupper side of the helicoid 58 to communicate with the passage 50 throughwhich plastic material is supplied to the crosshead assembly. Thismeeting of the branch passages 96 into a common passage at the end ofsupply passage 50 is indicated in the drawing by the reference character98. The way in which the common passage 98 divides to supply plasticmaterial 16' around both sides of the helicoid 58 is shown clearly inFIG. 7. Each of the passages 96 extends substantially a quarter of theway around the helicoid 58 so that the passages 96 terminate on oppositesides of the helicoid as also shown in FIG. 7.

Referring to FIGS. 3 and 5, the passages 96 extend to the right in thedrawing as they extend circumferentially around the helicoid 58, andthese passages 96 have curved lower ends which meet passages 100 formedon both sides of the helicoid 58 by diverging grooves in the outsidecylindrical surface of the helicoid 58. These passages 100 increase incircumferential width as they extend toward the left in FIG. 3, that is,in a direction counter to the eventual direction of discharge of thematerial 16 from the die 82. This increase in width of the passages 100is shown clearly in FIG. 3.

In order to prevent excessive reduction in the velocity of the materialas it passes through the passages 100, these passages decrease in radialwidth as they extend toward the left as clearly shown in FIG. 5. Thusthe actual cross-section of the passages 100 need not changesubstantially throughout their length and this produces a more uniformrate of flow of the material.

The left hand end of the helicoid 58 is rounded, as shown in FIGS. 3 andand this rounded end face of the helicoid confronts complementaryrounded surfaces on the cross-head 56 and core guide 64so-as to providesubstantially 180 degree turn passages-102 which are annular in extent;that is, they are all around the circumference of the end of thehelicoid -58 and which form a common annular passage after theirindividual circumferential extent exceeds 180. The passages 100 cometogether at the point I04 on the far side of the cross-head assembly inFIG. 5 and at a corresponding point on the near side of the assemblyahead of the plane of section.

The plastic material after changing its direction of flow at the returnpassages 102 flows forward through an annular passage indicated by thereference charac- I ter 108 and formed by an annular clearance betweenthe core guide 64 and first the helicoid 58, then the tapered fillerelement 94 and finally the face of the extruded die 82. v

In the construction illustrated, the passage 108 increases somewhat inradial width to compensate for its decrease in circumferential width asit converges toward the core 88. At the die 82, the passage for theplastic compound decreases in cross-section to provide a covering of thedesired thickness. The die 82 is replaced by other dies which producedie openings of different radial width depending upon the desiredcovering thickness, in accordance with conventional practice.

In the preferred construction, the cross-sectional area through whichthe compound flows is preferably constant throughout the flow path andby maintaining constant or substantially constant cross-sections of thecompound as it flows through the cross-head assembly, the velocity offlow is very nearly constant. Pressure drop due to frictional resistanceto flow is likewise very nearly a constant, thus insuring that thecompound velocity upon arriving at the die 82 is very nearly uniformabout .the circumference of the die thus producing a substantiallyperfectly concentric covering around the core.

It will be apparent that the correlation of the passages of the flowpath of this invention reduce the variation in length of flow path to aminimum. For example, the distance from point D in FIG. 3 to point E andthen by the reverse direction in flow to the forming die 82 is themaximum length of flow path. The distance from the point D to the pointF in FIG. 3 represents the minimum length of flow path. The influence ofpath length on flow rate is proportional to the ratio of the length ofthe paths involved. If both paths are relatively long, the influence offlow rate resulting from the difference in length diminishes as theoverall length of the path increases.

It would be a relatively simple matter to increase the length of theflow path shown in the drawing by increasing the length of the assembly,but the proportions illustrated result in so little difference in flowpath that the velocities at the die outlet are substantially uniformaround the-circumference of the core and'the eccentricity, if any,remains always well within acceptable limits.

One feature of the invention by which long flow paths are obtainedwithout resorting to excessive lengths of cross-head assembly is the useof the branch passages extending circumferentially around differentsides of the helicoid, and the use of passages extending lengthwisealong the helicoid for most of its longitudinal length in a directioncounter to the direction of movement of the core so that the movementback along this distance towards the die outlet provides a substantiallength much greater than the length of the helicoid. In the constructionillustrated the total lengthof the flow passage is substantially twicethe length of the helicoid.

There are sometimes imperfections inadvertently incorporated in thecomponents of a cross-head during manufacture. This may affect the flowof the plastic compound 16' along the flow path. The effect of theseimperfections can be compensated by adjusting the screws 74 to offsetthe core guide 64 to some extent with respect to the confronting face ofthe helicoid 58. This adjustment of the core guide increases thecrosssection of the flow path on one side and reduces it on the otherand can be used to compensate imperfections in the parts of the assemblywhich result in eccentricity of the coating 86.

The preferred embodiment of the invention has been illustrated anddescribed but changes and modifications can be made and some featurescan be used in different combinations without departing from theinvention as defined in the claims.

What is claimed is:

1. An extruder cross-head assembly for extruding a jacket or coveraround a traveling core including in combination a guide through whichthe core passes, a supply passage through which covering material issupplied to the cross-head assembly at high temperature and pressure,branch passage leading from the supply passage circumferentially tolocations on opposite sides of the core guide, a longitudinallyextending passage having separate parts communicating with the branchpassages at said locations, said longitudinally extending passageextending first rearwardly counter to the direction of movement of thecore and then forwardly in the direction of movement of the core, theseparate parts of said longitudinally extending passage diverging togreater circumferential angular width as they extend away from saidbranch passages and eventually combining with one another to surroundthe full circumferential angular extent of the core guide, and a dieinto the longitudinally extending passage discharges covering materialat substantially uniform velocity around the circumferential extent ofthe traveling core.

2. The extruder cross-head assembly described in claim 1 characterizedby each of said separate parts of the longitudinally extending passagediverging to a circumferential extent of 180 so that they meet andembrace a 360 extent of discharge for the covering material within thedistance that said separate parts of the passage extend in directionscounter to the direction of movement of the core.

3. The extruder cross-head assembly described in claim 1 characterizedby the branch passages extending in directions that have a componentwhich is parallel to the direction of movement to the core through thecross-head assembly.

4. The extruder cross-head assembly described in claim 1 characterizedby the cross-head assembly including a cross-head, a helicoid within thecross-head and surrounding the core guide, the branch passages havinggrooves in the helicoid that are closed along most of their length byoverlying surfaces of the crosshead, the supply passage opening throughthe crosshead into communication with the branch passages where theycome together.

5. The extruder cross-head assembly described in claim 1 characterizedby the sum of the cross sections of the branch passages, the combinedcross sections of the separate parts of the longitudinally extendingpassages, ard the rest of the longitudinally extending passage to theregion of an extrusion die being the same cross-section so that thevelocity of the coating material and the pressure drop therein issubstantially uniform throughout the flow path of the coating materialthrough the cross-head assembly.

6. The cross-head assembly described in claim 5 characterized by theradial depth and circumferential 'width of the various portions of thepassages varying oppositely to maintain the cross-sections of the flowpath substantially equal along the full length thereof from the supplypassage to the entrance into the extruder die.

7. The extruder cross-head assembly described in claim 1 characterizedby the cross-head assembly including a helicoid with surfaces that formpart of the wall of the branch passages and the longitudinally extendingpassage throughout most of the length of said passages, the length ofthe flow passages for the coating material being greater than the lengthof the helicoid in a direction parallel to the direction of movement ofthe core.

8. The extruder cross-head assembly described in claim 7 characterizedby the branch passages and the portion of the longitudinally extendingpassage that extends in a direction counter to the'direction of movementof the core being grooves in the outside surface of the helicoid, andthe portion of the longitudinally extending passage that extends in thedirection of the movement of the core being formed by a clearancebetween the helicoid and the core guide, the combined length of eitherof the branch passages and the longitudinally extending passage beingmore than twice as long as the helicoid in the direction of movement ofthe core.

9. The extruder cross-head assembly described in claim 1 including across-head having a bore opening therethrough and longitudinallythereof, a helicoid that fits within the bore and that itself has alongitudinal bore extending therethrough, the core guide having anoutside surface that confronts the wall of the bore through thehelicoid, grooves in the outside surface of the helicoid forming withother overlying surface areas of the cross-head the separate parts ofthe longitudinally extending passage that extend in a direction counterto the direction of movement of the core, the limit of extent of thehelicoid in a direction counter to the direction of movement of the corebeing spaced from the cross-head and from one end of the core guidearound the full circumference of the helicoid to provide an annularportion of the longitudinally extending passage, a portion of thepassage that curves from a rearwardly extending direction to a forwardlyextending position, the helicoid having an underside surface spaced fromthe core guide and providing a portion of the forwardly extending lengthof the longitudinally extending passage, and an extruder die confrontingthe other end of the core guide and having clearance from the diethrough which coating material is extruded over the traveling core.

10. The extruder cross-head assembly described in claim 9 characterizedby a counter bore in the crosshead that holds a part of the core guidethat is remote from the die end of the core guide, the counter borehaving an inside diameter larger than the outside diameter of anadjacent part of the core guide, and adjusting screws at angularlyspaced locations around the counter bore and threaded through thecross-head into contact with the core guide for adjusting the alignmentof the core guide with respect to the helicoid to alter the clearancebetween the confronting faces of the helicoid and the core guide and theresulting radial depth of the longitudinally extending passage on thedifferent sides thereof.

* 0 t t 0K

1. An extruder cross-head assembly for extruding a jacket or coveraround a traveling core including in combination a guide through whichthe core passes, a supply passage through which covering material issupplied to the cross-head assembly at high temperature and pressure,branch passage leading from the supply passage circumferentially tolocations on opposite sides of the core guide, a longitudinallyextending passage having separate parts communicating with the branchpassages at said locations, said longitudinally extending passageextending first rearwardly counter to the direction of movement of thecore and then forwardly in the direction of movement of the core, theseparate parts of said longitudinally extending passage diverging togreater circumferential angular width as they extend away from saidbranch passages and eventually combining with one another to surroundthe full circumferential angular extent of the core guide, and a dieinto the longitudinally extending passage discharges covering materialat substantially uniform velocity around the circumferential extent ofthe traveling core.
 2. The extruder cross-head assembly described inclaim 1 characterized by each of said separate parts of thelongitudinally extending passage diverging to a circumferential extentof 180* so that they meet and embrace a 360* extent of discharge for thecovering material within the distance that said separate parts of thepassage extend in directions counter to the direction of movement of thecore.
 3. The extruder cross-head assembly described in claim 1characterized by the branch passages extending in directions that have acomponent which is parallel to the direction of movement to the corethrough the cross-head assembly.
 4. The extruder cross-head assemblydescribed in claim 1 characterized by the cross-head assembly includinga cross-head, a helicoid within the cross-head and surrounding the coreguide, the branch passages having grooves in the helicoid that areclosed along most of their length by overlying surfaces of thecross-head, the supply passage opening through the cross-head intocommunication with the branch passages where they come together.
 5. Theextruder cross-head assembly described in claim 1 characterized by thesum of the cross sections of the branch passages, the combined crosssections of the separate parts of the longitudinally extending passages,and the rest of the longitudinally extending passage to the region of anextrusion die being the same cross-section so that the velocity of thecoating material and the pressure drop therein is substantially uniformthroughout the flow path of the coating material through the cross-headassembly.
 6. The cross-head assembly described in claim 5 characterizedby the radial depth and circumferential width of the various portions ofthe passages varying oppositely to maintain the cross-sections of theflow path substantially equal along the full length thereof from thesupply passage to the entrance into the extruder die.
 7. The extrudercross-head assembly described in claim 1 characterized by the cross-headassembly including a helicoid with surfaces that form part of the wallof the branch passages and the longitudinally extending passagethroughout most of the length of said passages, the length of the flowpassages for the coating material being greater than the length of thehelicoid in a direction parallel to the direction of movement of thecore.
 8. The extruder cross-head assembly described in claim 7characterized by the branch passages and the portion of thelongitudinally extending passage that extends in a direction counter tothe direction of movement of the core being grooves in the outsidesurface of the helicoid, and the portion of the longitudinally extendingpassage that extends in the direction of the movement of the core beingformed by a clearance between the helicoid and the core guide, thecombined length of either of the branch passages and the longitudinallyextending passage being more than twice as long as the helicoid in thedirection of movement of the core.
 9. The extruder cross-head assemblydescribed in claim 1 including a cross-head having a bore openingtherethrough and longitudinally thereof, a helicoid that fits within thebore and that itself has a longitudinal bore extending therethrough, thecore guide having an outside sUrface that confronts the wall of the borethrough the helicoid, grooves in the outside surface of the helicoidforming with other overlying surface areas of the cross-head theseparate parts of the longitudinally extending passage that extend in adirection counter to the direction of movement of the core, the limit ofextent of the helicoid in a direction counter to the direction ofmovement of the core being spaced from the cross-head and from one endof the core guide around the full circumference of the helicoid toprovide an annular portion of the longitudinally extending passage, aportion of the passage that curves from a rearwardly extending directionto a forwardly extending position, the helicoid having an undersidesurface spaced from the core guide and providing a portion of theforwardly extending length of the longitudinally extending passage, andan extruder die confronting the other end of the core guide and havingclearance from the die through which coating material is extruded overthe traveling core.
 10. The extruder cross-head assembly described inclaim 9 characterized by a counter bore in the cross-head that holds apart of the core guide that is remote from the die end of the coreguide, the counter bore having an inside diameter larger than theoutside diameter of an adjacent part of the core guide, and adjustingscrews at angularly spaced locations around the counter bore andthreaded through the cross-head into contact with the core guide foradjusting the alignment of the core guide with respect to the helicoidto alter the clearance between the confronting faces of the helicoid andthe core guide and the resulting radial depth of the longitudinallyextending passage on the different sides thereof.